This research assesses prescribed burning as a habitat management
technique in wetlands and associated upland communities of Malheur
National Wildlife Refuge, southeastern Oregon. Experimental burns
were conducted to evaluate fire behavior and effects in wetland and
upland habitats, and, fire effects on Cirsium arvense. Wetland plant
communities were monotypic stands of emergent macrophytes: Scirpus
acutus, Sparganium eurycarpum, Carex atherodes, Juncus balticus,
Eleocharis palustris. Upland communities studied included
Chrysothamnus nauseosus/Elymus cinereus and Sarcobatus
vermiculatus/Distichlis spicata shrub-grasslands and an Elymus
triticoides mesic meadow. Burning was conducted during periods of
vegetation dormancy.
Stepwise multiple regression was used to evaluate the relative
influence of various fuel and weather parameters on fire behavior,
and, to quantify the relationship of the "best" independent variables
to the response variables rate-of-spread (ROS) and flame length.
Models incorporating windspeed alone, or in combination with a second
variable, account for 50 to 90 percent of the variation in ROS.
Successful burns were conducted with a wide range of conditions,
provided the surface of fuels were dry and winds were steady.
Burning prescriptions and techniques suitable for these fuel types are
given.
Fire effects on vegetation were measured for two years
(Sarcobatus/Distichlis, one year). Vegetation response was largely
insensitive to timing of burns within the dormant period. Comparisons
with unburned treatments (=non-use) indicate fire significantly alters
vegetation structure and community function; however, responses were
often species-specific. Aboveground herbage production increased for
one to two years in all but winter-burned Sparganium communities.
Burning increased shoot density of rhizomatous species. Vigorous
postburn sprouting-regrowth of shrubs resulted in rapid replacement
of canopy cover and volume. Reproductive effort varied markedly
among species and in response to fire. The observed dynamics of
organic residues suggest these communities will return to preburn
status after three to five years.
Dormant season burning reduced relative abundance of Cirsium
arvense. Changes in population structure and reproductive success, as
well as increased production of associated species, indicate burning
may be a useful means of halting Cirsium invasion or spread by
maintaining a productive stand of native vegetation.